Allow the promotion of entities from one environment to another

## Background
Currently there is no easy way to move entity definitions across environments. Recreating datasets by hand can be especially tedious.

## Feature
It would be great if we could push a button in Menas and promote datasets and their dependencies in bulk to another Menas server, (e.g, Test -> Dev -> UAT -> Pre-prod -> Prod).

An open question is how to handle conflicts (cases where a dataset in the remote environment already has a dataset with the same name and version). This conflict resolution should be drawn up in a shared doc and once resolved posted here.

This task is similar in nature to #34, but meant for direct promotion via HTTP and in bulk, while #34 is meant for manual single item import/export.